1. Field of the Invention
The present invention relates to an optical head driven by a predetermined driving mechanism to move close to a predetermined storage medium for applying beams of light to a surface of the storage medium, a lens used for such an optical head, and an optical memory apparatus for performing read and write of information to the storage medium using such an optical head.
2. Description of the Prior Art
Hitherto, there is known an optical memory apparatus in which an optical head as mentioned above is used to condense beams of light on a storage medium so that a condensed spot is formed on the storage medium, and the condensed spot is used to write information into the storage medium by means of heating the storage medium, or the condensed spot is used to read information from the storage medium. Recording density of information by such an optical memory apparatus is higher with the smaller diameter of the condensed spot.
According the conventional optical memory apparatus, it is general to use an optical head in which a condensing system such as a condensing lens is used to form a condensed spot. However, it is difficult to reduce a diameter, of the condensed spot formed by the condensing system less than a size referred to as a diffraction limit which will be described later.
On the other hand, there is a proposed technology wherein a specific condensing system, which is small in the diffraction limit per se, is used to record information with greater density, and a technology wherein an optical fiber and the like is processed to form a microscopic emitting outlet so that a small size of the condensed spot is physically formed.
Recently, it is desired to greatly increase the recording density of information read and written by the optical memory apparatus. Thus, there is desired a technology of implementing a spot of which diameter is smaller than a wavelength of a laser beam. However, according to the above-mentioned technology using the specific condensing system, a diameter of the spot is simply reduced to the extent of the wavelength of a laser beam. And, according to the above-mentioned technology using the microscopic emitting outlet, it is difficult to form an emitting outlet smaller than the wavelength of a laser beam per se.
In view of the foregoing, it is an object of the present invention to provide an optical head capable of forming a condensed spot of which a diameter is smaller than a wavelength of light and is easily fabricated, a lens suitable for such an optical head, and an optical memory apparatus for performing read and write of information to a storage medium with high density.
To achieve the abode-mentioned objects, the present invention provides an optical head applying beams of light to a surface of the storage medium, said optical head comprising:
a light emission unit for emitting a light beam;
an optical part having an incident surface onto which light beam is incident and an exit surface from which the light beam applied through the incident surface is emitted; and
a transmission unit permitting part of a predetermined optical intensity or more of the light beam emitted from the exit surface of said optical part to pass through said transmission unit.
In the optical head as mentioned above, it is acceptable that said transmission unit is made of a material in which part of an incident light energy is converted into a thermal energy, said material permitting an incident light to be transmitted at higher transmittance with higher temperature. Or alternatively, it is acceptable that said transmission unit is made of a saturable absorber having properties in which an absorbency index is lowered in accordance with an increment of an incident light intensity.
According to the optical head of the present invention, the exit surface is covered by the transmission unit as mentioned above. Consequently, of the light beam, applied to the exit surface, only part of the high optical intensity is transmitted through the transmission unit. Thus, when the light beam, stopped up to a wavelength or so by an optical system, is applied to the exit surface, as will be described later, a condensed spot of which a diameter is smaller than the wavelength is formed by the transmission unit. The transmission unit as mentioned above can be easily formed, for example, in such a manner that the exit surface is subjected to a coating treatment in the form of a transmission film. Further, it is acceptable that the transmission unit is formed as a sheet provided apart from the exit surface. Or alternatively, it is acceptable that the transmission unit is formed as a layer by processing the optical part itself.
In the optical head as mentioned above, it is acceptable that the optical part establishes a focus of the light beam on said exit surface. Or alternatively, it is acceptable that the optical part is an optical fiber.
In case of the optical head using the optical fiber, it is desired that the optical fiber has said exit surface on one end of said optical fiber, said optical fiber having a configuration tapered toward the one end.
This feature makes it possible to form a condensed spot which is high in light intensity.
Further, in case of the optical head using the optical fiber, it is desired that said optical fiber has a projecting exit surface on one end of said optical fiber.
This feature makes it possible to form a condensed spot which is high in light intensity.
To achieve the above-mentioned objects, the present invention provides a first optical part comprising:
an optical part comprising:
an incident surface onto which a light beam is incident;
an exit surface from which the light beam applied through said incident surface is emitted; and
a transmission unit permitting part of the light beam emitted from the exit surface to be transmitted at higher transmittance with higher light intensity.
To achieve the above mentioned objects, the present invention provides an optical part comprising an incident surface onto which a light beam is incident, and an exit surface from which the light beam applied through said incident surface is emitted,
wherein a transmission layer, which permits part of a predetermined optical intensity or more of the light beam to pass through said transmission layer, is provided on said exit surface.
In connection with an optical part of the present invention, it is acceptable that the optical part is a lens or an optical fiber.
To achieve the above-mentioned objects, the present invention provides a first optical memory apparatus comprising:
an optical memory apparatus comprising:
a light emission unit for emitting a light beam;
an optical part having at least a transmission unit permitting part of a predetermined optical intensity or more of the light beam emitted from the light emission unit to pass through said transmission unit;
a storage medium holding mechanism for holding a storage medium, to which the part of the light beam is applied, at a predetermined position; and
an optical part driving mechanism for driving said optical part.
According to the first optical memory apparatus, it is possible to perform read and write of information at high density by a condensed spot having a diameter smaller than a wavelength of light.
In the first optical memory apparatus as mentioned above, it is acceptable that said optical part driving mechanism drives the optical part in a state that the storage medium is held, and that the storage medium holding mechanism and the transmission unit are spaced from one another by a length not more than a wavelength of the light beam.
Further, in the first optical memory apparatus mentioned above, it is acceptable that said transmission unit is made of a material in which part of an incident light energy is converted into a thermal energy, said material permitting an incident light to be transmitted at higher transmittance with higher temperature. Alternatively, it is acceptable that said transmission unit is made of a saturable absorber having properties in which an absorbency index is lowered in accordance with an increment of an incident light intensity.
Further, in the first optical memory apparatus as mentioned above, it is acceptable that the optical part establishes a focus of the light beam on said exit surface. Alternatively, it is acceptable that the optical part is an optical fiber.
Further, to achieve the above-mentioned objects, the present invention provides a second optical memory apparatus comprising:
an optical memory apparatus comprising:
a light emission unit for emitting a light beam;
an optical part having an incident surface onto which the light beam is incident, and an exit surface from which the light beam applied through the incident surface is emitted, said optical part being formed so as to condense the light beam on the exit surface and having numerical aperture not more than 0.75;
a storage medium holding mechanism for holding a storage medium, to which the light beam is applied, at a predetermined position; and
an optical part driving mechanism for driving said optical part in a state that the storage medium held by said storage medium holding mechanism and said exit surface are spaced from one another by a length not more than one-tenth of a wavelength of the light beam.
According to the second optical memory apparatus, as will be described later, even if a length between the exit surface and a surface of the storage medium is varied, a quantity of light irradiated onto the storage medium is stable. This feature makes it possible to perform a stable read and write of information for a storage medium and also to perform read and write of information at high density.
In the second optical memory apparatus as mentioned above, it is acceptable that said optical part has a transmission unit permitting part of a predetermined optical intensity or more of the light beam emitted from the light emission unit to pass through said transmission unit.
In case if the second optical memory apparatus using the optical part having the transmission unit, it is acceptable that said transmission unit is made of a material in which part of an incident light energy is converted into a thermal energy, said material permitting an incident light to be transmitted at higher transmittance with higher temperature. Alternatively, it is acceptable that said transmission unit is made of a saturable absorber having properties in which an absorbency index is lowered in accordance with an increment of an incident light intensity.